The 2003 Presidential Commission Report on the Future of the USPS concluded that the Postal Service should continue to develop effective merging systems that optimize efficiency, e.g., maximize the number of mailpieces shipped with each mile traveled, while minimizing the labor content associated with mailpiece handling. With respect to the latter, all elements of the mail stream (letters, flats, periodicals, post cards, etc.) should be sorted, merged, and/or sequenced at a centralized location with the expectation that no subsequent handling would be required at each of the local postal branch offices, other than the physical delivery to the recipient address.
Most postal services are actively exploring opportunities to reduce the overall cost of processing mail by investing in postal automation equipment and employing state-of-the-art materials management techniques to improve efficiencies in the various process steps. In some instances, the savings from automation equipment may be, unfortunately, offset by increases in transportation costs.
Sorting equipment typically loads mailpieces by a gravity feed chute which drops mailpieces vertically into mail trays arranged below the chute. Occasionally, especially as the mail trays are nearly completely filled, portions of the mailpieces do not settle properly and partially protrude/extend above the top of the tray. As such, a substantial risk is incurred that the protruding mailpiece will catch on mechanisms related to the automated processing equipment, e.g., one of the tray transporting, storing, and/or retrieving systems. It will, therefore, be appreciated that such interference can damage the mailpiece or, alternatively, require system shut down to rectify the problem/obstruction. Further, the overall efficiency of the mail sortation system is adversely affected by these stacking errors.
Stacking errors can occur as a result of a variety non-optimum conditions and/or under a variety of circumstances. In one instance, a non-uniform thickness profile of the stacked envelopes can lead to one side of the stack being higher in the tray than the opposing side. In yet other instances, the stacking of mixed mail, e.g., a combination of flats-, letter-, and postcard-sized mailpieces, can result in a similar inconsistent or non-level stack profile. It will be appreciated that when mixed mail is aligned along at least one edge, letter and postcard-sized envelopes, which may be less than one-half the length of flats mailpieces, will leave a thickness void in regions where a flat envelope would otherwise extend the full length and maintain uniform thickness of the stack.
To address the difficulties associated with stacking errors, mailpiece equipment manufacturers have typically employed one of two known methods/solutions. Firstly, the tray capacity may be limited to about 70% of the total potential capacity. As such, the probability that a mailpiece will protrude beyond the bounds of the container is significantly diminished. Many of the current sorters are equipped with sensors to determine when the height of the mailpiece stack reaches seventy percent (70%) of full level. Secondly, sensors may be deployed throughout the tray transport system to detect when or if mailpieces protrude beyond the top of the container/tray. Trays which have been over-filled are typically diverted to a secondary track for an operator to manually correct the stacking error and return the tray to the primary or principle track.
While these solutions eliminate difficulties associated with equipment jamming or malfunction, the mailpiece container trays are not filled to full capacity. As a result, the containers are shipped with thirty percent (30%) of its volume in air rather than in mailpiece content material. Additionally, the labor cost in operating multi-million dollar sorting equipment remains high due to the human intervention required to correct the stacking errors.
A need, therefore, exists for a system and method to accommodate mixed mail, including mail of inconsistent thickness, to optimally fill mail containers/trays.